mysql - 如何在 MySQL 中执行 "horizontal UNION"？ (连接表格)

Question

我正在寻找连接或合并两个(或更多)表的可能性。我无法加入所有表，因为没有引用和没有匹配的列。如果我在没有任何“ON”的情况下加入，我将得到表 1 中的所有数据乘以表 2 中的所有数据(不是我想要的)。所以我试图用 MySQL 用户定义的变量提供假的 rownums，但由于所有表中的数据量不同，我无法比较它们。这有点难以解释。因此，我将提供一些示例。

示例 1(表 1 = 4 行，表 2 = 3 行，结果 = 4 行)

+---------+---------+---------------+
| Table 1 | Table 2 | Result        |
+---------+---------+-------+-------+
| Col 1   | Col 1   | Col 1 | Col 2 |
+---------+---------+-------+-------+
| A       | H       | A     | H     |
| B       | I       | B     | I     |
| C       | J       | C     | J     |
| D       |         | D     | NULL  |
+---------+---------+-------+-------+

示例 2(表 1 = 3 行，表 2 = 4 行，结果 = 4 行)

+---------+---------+---------------+
| Table 1 | Table 2 | Result        |
+---------+---------+-------+-------+
| Col 1   | Col 1   | Col 1 | Col 2 |
+---------+---------+-------+-------+
| A       | H       | A     | H     |
| B       | I       | B     | I     |
| C       | J       | C     | J     |
|         | K       | NULL  | K     |
+---------+---------+-------+-------+

示例 3(表 1 = 3 行，表 2 = 4 行，表 3 = 2 行，结果 = 4 行)

+---------+---------+---------+-----------------------+
| Table 1 | Table 2 | Table 3 | Result                |
+---------+---------+---------+-------+-------+-------+
| Col 1   | Col 1   | Col 1   | Col 1 | Col 2 | Col 3 |
+---------+---------+---------+-------+-------+-------+
| A       | H       | O       | A     | H     | O     |
| B       | I       | P       | B     | I     | P     |
| C       | J       |         | C     | J     | NULL  |
|         | K       |         | NULL  | K     | NULL  |
+---------+---------+---------+-------+-------+-------+

现在是真正困难的部分。我需要这个作为查询。我不想填充其他临时表。如果可能:-)

Answer 1

我认为您是在按“Col 1”值简单排序的每个表的密集序数排名中加入？

这实际上是按每个表的等级进行的完全外部联接。

不幸的是，MySQL 不支持 ROW_NUMBER() 分析函数，这将使这个相对简单:

SELECT *
FROM (SELECT "Col 1", ROW_NUMBER() (OVER ORDER BY "Col 1") AS RowNum FROM "Table 1") AS T1
FULL OUTER JOIN (SELECT "Col 1", ROW_NUMBER() (OVER ORDER BY "Col 1") AS RowNum FROM "Table 2") AS T2
    ON T2.RowNum = T1.RowNum
FULL OUTER JOIN (SELECT "Col 1", ROW_NUMBER() (OVER ORDER BY "Col 1") AS RowNum FROM "Table 3") AS T3
    ON T3.RowNum = T2.RowNum
ORDER BY COALESCE(T1.RowNum, T2.RowNum, T3.RowNum)

MySQL 中有替代方案，但我不熟悉解决方法。

就 FULL OUTER JOIN 解决方法而言，排名很容易，因为已知排名只是自然数:

SELECT *
FROM Numbers
LEFT JOIN (SELECT "Col 1", ROW_NUMBER() (OVER ORDER BY "Col 1") AS RowNum FROM "Table 1") AS T1
    ON T1.RowNum = Numbers.Number
LEFT JOIN (SELECT "Col 1", ROW_NUMBER() (OVER ORDER BY "Col 1") AS RowNum FROM "Table 2") AS T2
    ON T2.RowNum = Numbers.Number
LEFT JOIN (SELECT "Col 1", ROW_NUMBER() (OVER ORDER BY "Col 1") AS RowNum FROM "Table 3") AS T3
    ON T2.RowNum = Numbers.Number
WHERE COALESCE(T1.RowNum, T2.RowNum, T3.RowNum) IS NOT NULL
ORDER BY Numbers.Number